1. Field of the Invention
This invention relates to a method of rolling an elongated metal preform, such as a continuously cast thin slab, to form strip; more particularly, to a method for finish rolling contiguous segments of the elongated preform in a single rolling mill stand.
2. Description of the Prior Art
Since the advent of the continuous casting of molten metals, workers in the art have sought ways to process the continuous strand of solidified metal in an "in-line" manner to produce useful, finished metal products with as few interruptions and ancillary processing steps as possible. An example of these development efforts may be found in the production of hot rolled steel strip.
Continuously cast slabs had earlier been the starting material for hot rolled strip products; these slabs had to be heated to rolling temperature and then subjected to a two stage rolling process. The first stage involved preliminary reduction in a series of strong roughing stands for rolling the relatively thick slabs; then the material was finished in a string of final rolling stands. Obviously, the cost of the equipment and indoor space required for this two stage rolling of hot strip makes the procedure unattractive.
In order to eliminate the need for roughing stands, having a thickness in the range of about 3/4" to 1.5" and a width ranging up to about 60 inches. The thin slab can be hot rolled directly into strip products, thereby eliminating the production of conventional slabs and their associated preliminary rolling. But with this advance came a new series of problems brought about by the fact that maximum casting speed at which the thin slab leaves the continuous casting machine is much lower than the minimum possible rolling speed of conventional hot rolling mills. Workers in the art compensated for the differential in casting and rolling speeds by shearing the thin slab to form discrete elongated pieces which were coiled and held for subsequent hot rolling at the higher speeds in mills such as tandem finishing mills having 5 to 6 stands in series; reversing mills such as the Steckel mill that requires elaborate coil heating furnaces at both ends; and planetary mills which produce a scalloped surface on the rolled material, thereby making necessary a flattening pass through an additional roll stand. All of these known finishing mills are costly and require considerable maintenance.
The present invention, as applied to hot rolling, accepts the relatively slow speeds of production from the thin slab casting machine and seeks to match the hot rolling speed with them. This technique permits the use of a relatively simple, inexpensive single mill stand. The space required for the practice of the present invention is small compared with known hot strip plants.
Thus, in one embodiment of the present invention, the strand of thin slab from the continuous caster can be processed through the hot rolling mill without interruption. The invention also may be used advantageously to hot or cold roll discrete coils of thin metal slab; further billets or shapes having curved cross sections such as rounds and ovals may be rolled by the practice of the present invention.